1. Field of the Invention
The present invention relates to a liquid ejection head, an image forming apparatus and a method of manufacturing a liquid ejection head, and more particularly to a liquid ejection head, an image forming apparatus and a method of manufacturing a liquid ejection head that can achieve a high-density arrangement of ejection ports ejecting a liquid while also permitting ejection of high-viscosity liquid.
2. Description of the Related Art
An inkjet type image forming apparatus has a print head (liquid ejection head) in which a plurality of nozzles (ejection ports) are arranged in the form of a matrix, and it forms an image on a recording medium by ejecting ink droplets from the nozzles onto the recording medium.
According to an internal structure of a conventional print head, it is known that a plurality of pressure chambers connected to a plurality of nozzles; a common liquid chamber which stores an ink; a plurality of ink supply ports which supply the ink from the common liquid chamber to the pressure chambers; and the nozzles are disposed on the same side of a diaphragm which forms one surface of the pressure chambers. Those piezoelectric elements are disposed on the opposite side to the diaphragm. When the ink is supplied from the common liquid chamber to the pressure chambers and an electrical signal corresponding to the image data is applied to a piezoelectric element, then the piezoelectric element is driven and the diaphragm forming a portion of the corresponding pressure chamber is caused to deform. Thereby, since the volume of the pressure chamber decreases, then the ink inside the pressure chamber is ejected from the nozzle in the form of an ink droplet. When the ink droplet lands on the recording medium, it forms a dot on the recording medium. By combining dots of this kind, an image is formed on the recording medium.
In recent years, there have been demands for improved image quality in inkjet type image forming apparatuses. In order to improve image quality, it is necessary for reducing the size of the ink droplets ejected from the nozzles, by reducing the diameter of the nozzles, while also increasing the number of pixels per image by arranging the nozzles at a high density in the print head. Accordingly, in the prior art, various technologies have been proposed with the aim of increasing nozzle density (see Japanese Patent Application Publication Nos. 9-226114, 2001-179973, 2000-127379, 2000-289201, and 2003-512211, for example).
Japanese Patent Application Publication No. 9-226114 discloses a print head having a structure in which a plurality of holes for supplying ink are formed in a diaphragm, which a reservoir (common liquid chamber) is disposed on the opposite side of the diaphragm with respect to the nozzles.
Japanese Patent Application Publication No. 2001-179973 discloses a print head having a structure in which an ink supply section (common liquid chamber) is provided on the piezoelectric element side of a diaphragm, which an ink supply port is formed on the outside region of a pressure generating chamber (pressure chamber) of a diaphragm.
Japanese Patent Application Publication No. 2000-127379 discloses a print head having a reservoir section (common liquid chamber) formed on a surface on which piezoelectric elements are formed.
Japanese Patent Application Publication No. 2000-289201 discloses a print head in which piezoelectric elements are disposed on the side of pressure chambers adjacent to the nozzles, and a substrate (wiring layer) is disposed on the opposite side with respect to the nozzles.
Japanese Patent Application Publication No. 2003-512211 discloses a print head in which an ink supply layer comprised by a porous member for supplying the ink to pressure chambers is disposed between a nozzle layer in which nozzles are formed, and a cavity layer formed with ink cavities (pressure chambers). According to this reference, a plurality of piezoelectric elements are disposed on a displacement plate (diaphragm) which constitutes the ceiling of the ink cavities, a plurality of wiring members are provided from the piezoelectric elements in a substantially perpendicular direction with respect to the nozzle surface, and a substrate (wiring layer) is disposed at the ends of those wiring members.
However, if the density of the nozzles is increased in a conventional print head composition, there is a problem in that the electrical wires cannot be patterned onto the same surface as in the prior art, due to the increase in the number of electrical wires, such as the wires of the piezoelectric elements.
For example, the electrical wires of the print heads disclosed in Japanese Patent Application Publication Nos. 9-226114 and 2001-179973 are formed on a diaphragm. Thereby, when the nozzles are formed to high density, it is difficult to ensure sufficient space for the electrical wires.
Furthermore, the wiring of the print head disclosed in Japanese Patent Application Publication No. 2000-127379 is formed by wire-bonding, film formation, or the like. However, the wiring does not envisage a matrix-type nozzle arrangement, and hence it is difficult to position wiring of this kind at high density.
In the print head disclosed in Japanese Patent Application Publication No. 2000-289201, since an electrical wiring layer is provided on the opposite side to the piezoelectric elements with respect to the pressure chambers, then sufficient space is ensured for the electrical wiring. However, electrodes (aluminum plugs) for connecting the piezoelectric elements with the wiring layer are formed in the laminated plates which constitute the print head. Therefore, when the density of the nozzles is increased, it is necessary for reserving a larger space for the electrodes, and hence there are restrictions on the design of the common liquid chamber provided in the print head. For example, in the case in which the common liquid chamber is reduced in size, when a large number of nozzles are driven at a high frequency, the ink supply from the common liquid chamber to the respective pressure chambers cannot keep up with the demand, and hence it becomes impossible to eject ink droplets from the nozzles.
In the print head disclosed in Japanese Patent Application Publication No. 2003-512211, since a common liquid chamber (ink manifold) which accumulates ink to be supplied to the ink supply layer is provided on the opposite side to the wiring layer with respect to the wiring members, the flow path for supplying ink to the pressure chambers from the common liquid chamber via the ink supply layer is long. Therefore, when the density of the nozzles is increased, there is a risk that the speed of ink supply will not be sufficient. In particular, since the ink supply layer is constituted by a porous member, the print head is not suitable for ejection of high-viscosity ink. Additionally, since the common liquid chamber is disposed as described above, no consideration is given to insulating the wiring members with respect to liquid.